Johan Bengtsson Wang Yi Timed Automata: Semantics, Algorithms and Tools. 87-124 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3098&spage=87 2003 conf/ac/2003pn Lectures on Concurrency and Petri Nets db/conf/ac/acpn2003.html#BengtssonY03